Arteriovascular disease continues to be a leading cause of morbidity and mortality among adults in Europe and North America. Although age-adjusted death rates have declined over the past two decades, the absolute mortality rate from arteriovascular disease has not. Arteriovascular disease accounts for over one-half million deaths (1 out of every 5) in the U.S. yearly. The lifetime risk of arteriovascular disease after age 40 has been estimated at 49% for men and 32% for women. Even for those who survive to age 70 years, the lifetime risk for arteriovascular disease has been estimated at 35% for men and 24% for women. Arteriovascular diseases include atherosclerosis and atherothrombosis, coronary artery disease (CAD), peripheral artery disease (PAD), and cerebrovascular disease (CVD).
Risk factors for arteriovascular disease currently account for a large proportion of the burden of heart disease in the United States, suggesting that risk-factor identification and risk-lowering treatments could postpone or prevent the majority of ateriovascular events. Identified risk factors for arteriovascular disease include independent risk factors, such as cigarette smoking, elevated blood pressure (hypertension), elevated serum total cholesterol (CHOL) and low-density lipoprotein (LDL) cholesterol, low serum high-density lipoprotein (HDL) cholesterol, diabetes mellitus, and advancing age. Conditional risk factors for arteriovascular disease include elevated serum triglycerides (TRIG), small LDL particles, elevated serum homocysteine levels, elevated serum lipoprotein (a) (LPA), prothrombotic factors such as fibrinogen (FGA), and inflammatory markers like C-reactive protein (CRP), whose contribution to risk may vary upon their relationship to other identified risk factors. Other risk factors include obesity (measured by weight (WT), height (HT), Body Mass Index (BMI), and abdominal girth comparisons such as waist (“Waist”) or hip (“Hip”) circumference, ankle-brachial index, physical inactivity, family history of arteriovascular disease, ethnicity, and psychosocial factors. Arteriovascular disease risk factors have been the subject of many studies, including those presented in Pasternak, R. C. et al (2003) JACC 41(11): 1855-1917 and Grundy, S. M. (1999) Circulation 100: 988-998.
Typically, a patient suspected of having arteriovascular disease is assessed on several of the “traditional” or “conventional” risk factors: age, sex, total cholesterol concentration, HDL and LDL cholesterol concentration, smoking status, diabetic status, and blood pressure (systolic and diastolic), as well as many of the above conditional risk factors, such as LPA, FGA, CRP, and homocysteine, amongst others. These risk factors have been incorporated into useful predictive models of future arteriovascular events, such as the Framingham Risk Score presented in Wilson, P. W, et al (1998) Circulation 97: 1837-1847, however this “evidence-based” multiple risk factor or “global risk assessment” approach is only moderately accurate for predicting short- and long-term risk of manifesting a major arteriovascular event, particularly an event such as acute coronary syndromes (ACS, comprising myocardial infarction and unstable angina), stroke or sudden death, in healthy populations or asymptomatic individuals. In particular, while such approaches may, at typical clinical measurement cut-off levels, be relatively sensitive to individuals who have multiple risk factors, experienced past arteriovascular events or who have already confirmed arteriovascular disease (who would be “true positives” if they subsequently experience an acute arteriovascular event), they suffer from specificity, also identifying large portions of the population who do not subsequently experience acute arteriovascular events (“false positives”). In the typical adult population, these algorithms yield many more false positives than true positives, particularly in the low (<6% ten year risk of an acute event) and intermediate risk (6-20% ten year risk of an acute event) populations that make up the majority of those tested. While performance metrics for global risk assessment indices may evidence high clinical utility in the population in which the index algorithm was trained, occasionally exhibiting an AUC as high as 0.8, but more commonly an AUC around 0.7 (Wilson et al. above reported 0.74 for men and 0.77 for females for the Framingham Risk Score), such predictive models show relatively low transferability between populations, which may differ based on genetic and other factors, and absent substantial recalibration and re-optimization, often the AUC will drop to below 0.65, as shown in the example. They also are often difficult for clinicians to effectively implement and perform within an active clinical environment, involving complex calculations and numerical manipulations.
Thus, the general concept of applying one or more biomarkers to the task of classifying current and predicting future arteriovascular disease or risk of future arteriovascular events is not new in the clinical practice, literature or patent art. Several specific biomarkers, biomarker combinations, and methods have been proposed over time, with limited adoption to date due to several issues including technical difficulty, analytical performance, clinical performance, reliability, and practical clinician application of complex algorithms combining more than one such biomarker. By way of example, Ridker, P. et al. in U.S. Pat. No. 6,040,147 dated Mar. 21, 2000, suggested the use of a marker of systemic inflammation (including the use of CRP, a cytokine or a cellular adhesion marker such as soluble ICAM-1) could be useful in assessing the risk profile of an apparently healthy individuals risk profile for developing a future myocardial infarction, either alone or in combination with traditional risk factors such as CHOL or HDLC; such use of CRP has now become routine. Schonbeck, U. et al., in U.S. Pat. No. 7,189,518 B2 dated Mar. 13, 2007, suggested similar usage for soluble CD40 ligand (CD40LG) in predicting future cardiovascular disorders, such as myocardial infarction or stroke, in apparently healthy individuals; this has not been clinically adopted due to inadequate performance as a single marker. Anderson, L. (2004) in J. Physiological Society 563.1: 23-60, suggested 177 individual candidate biomarker proteins with reported associations to cardiovascular disease and stroke that might be of use in constructing panels of disease-related proteins for several applications, including the anticipation of future myocardial infarction or stroke, if it were found that several of the biomarkers were independent and not strongly correlated with each other, and thus able to be combined together into panels and “composite indices” more useful than the information gathered from the single biomarkers used individually; beyond referencing the previously mentioned relationships with CRP and cholesterol, no such useful individual panel involving was disclosed by Anderson, and several technical barriers and shortcomings of existing multi-marker analytical techniques in future discovery of such multi-marker associations were mentioned. Puskas, R. et al., in US Patent Publication 2006/0078998 A1 published Apr. 13, 2006, disclosed an technical technique useful for such single or multiplexed biomarker single molecule counting in samples, and mentions a wide analytical range of potential biomarkers and functional biomarker groupings potentially useful in multiple diseases, including cardiovascular disease; no specific combination of biomarkers for predicting the future risk of arteriovascular events was mentioned, nor were all of the individual biomarkers of the current invention disclosed therein.
Tabibiazar, R. et al., in US Patent Publication 2007/0070099239 A1 published May 3, 2007, disclosed the use of several specific panels of biomarkers combined with various algorithms and analytical processes, in the discrimination and classification of atherosclerotic patients with past acute myocardial infarction from such patients with known stable cardiovascular disease, from those with no history of cardiovascular disease or atherosclerosis, or amongst various classification of atherosclerotic staging and current medication use within known atherosclerotic patients. Although various “predictive” algorithms are mentioned therein, and the suggestion made that certain of such disclosed biomarker panels may be useful in the prediction of future cardiovascular events, no specific panel for prediction of future cardiovascular events or future cardiovascular status tested within an asymptomatic and previously undiagnosed population is disclosed. Nor is such clearly claimed in the application as filed, nor are any examples given within the published patent of study designs involving the measurement of apparently healthy and asymptomatic individuals prior to known cardiovascular events (or confirmed symptoms and/or diagnosed atherosclerosis) and then subsequently following their health status for a sufficient longitudinal time period allowing the development of subsequent cardiovascular events. Although certain of the individual panels of biomarkers disclosed therein may be useful in such applications, it is unlikely that the panels, algorithms and analytical processes disclosed therein, selected and trained on past events and known symptomatic disease, will successfully predict the future risk of cardiovascular events in asymptomatic and previously undiagnosed subjects with as high a degree of diagnostic accuracy as is presented and claimed in Tabibiazar over a specific multi-year time horizon, absent substantial and predictive model re-training, re-modeling, optimization and re-purposing likely not possible absent inputs from such longitudinal studies, which may include changes to cutoffs, reference values and other formula. Although overlap of certain individual biomarkers disclosed in Tabibiazar with individual biomarkers and a subset of the panels of the current invention is acknowledged, each of the individual biomarkers mentioned in Tabibiazar which are also claimed herein in specific panel combinations of the current invention (and specifically CCL2, IGF1, LEP, VEGF, and IL8) were also previously disclosed in the prior published art as associated with cardiovascular disease (each of them were notably mentioned and reviewed in the aforementioned Anderson reference, amongst others). Such specific clinical applications, additional biomarkers, specific biomarker combination panels, study designs, and analytical techniques and formula are key aspects of the current invention.
Recently, several studies in the scientific literature have been published examining various individual and multiple biomarker strategies, most notably Folsom, A. R. et al. (2006) Arch. Intern Med 166:1368-1373 and Wang, T. J. et al. (2006) N Eng J Med 355: 2631-2639. These studies, utilizing retrospective samples from longitudinal clinical studies such as the Atherosclerosis Risk in Communities Study and the Framingham Heart Study, combined subject clinical parameters and traditional laboratory risk factors (including using such traditional laboratory based biomarkers such as CHOL, CRP, FGA, HDLC, LPA, and Homocysteine), as well as novel markers such as Albumin-to-creatine ratios, Aldosterone, ANP (NPPA), BNP (NPPB), D-dimer, ICAM1, IL6, LEP, MMP1, PLA2G7, PLAT, PLG, REN, SELE, SERPINE1, TIMP1, THBD, amongst others, both as individual markers and incrementally as additions to multi-marker indices. Both studies found little improvement in the ability to predict future arteriovascular events with novel markers over the models incorporating the basic clinical parameters and traditional laboratory risk factors. As a result, the use of such novel markers remains clinically controversial.
Given the foregoing, it is clear that an important discrepancy has arisen in understanding the role of the aforementioned risk factors and biomarkers compared to the development of arteriovascular disease events. In contrast to the relative ease of recognition and clarity of treatment and prevention strategies in patients with symptomatic arteriovascular disease (i.e., exhibit symptoms such as active chest pain, claudication, transient ischemic attacks (TIAs) or mild cognitive impairment (MCI), a major problem of detection, treatment, and prevention of arteriovascular disease exists in the large, apparently healthy, population who have no symptoms, yet are at an increased risk to develop arteriovascular disease or experience major arteriovascular events. A large number of victims of the disease who are apparently healthy die or have initial acute arteriovascular events suddenly without prior symptoms. Despite the many available risk assessment approaches, a substantial gap remains in the detection of asymptomatic individuals who ultimately develop arteriovascular disease. Currently available screening and diagnostic methods are insufficient to identify asymptomatic individuals before such acute events associated with arteriovascular disease occur. Of those who experience a major arteriovascular event as many as 20% have none of the traditional risk factors. There remains an unmet need in the art to directly diagnose and predict the risk of arteriovascular disease and events, particularly in those individuals who do not exhibit symptoms or few or none of the traditional risk factors currently measured by physicians.
All of the foregoing references, including Tabibiazar, are herein referred to and incorporated in their entirety.